Typhoid Mary is an enemy and former lover of Daredevil with psionic powers, including telekinesis. She is also truly gravely mentally ill, and not entirely responsible for her actions as a result.

Suffering from dissociative identity disorder, Mary Walker has 3 other abnormal personalities in addition to her seemingly healthy one. Her "Mary" personality is a timid, quiet, pacifist; her "Typhoid" personality is adventurous, lustful, and violent; and her "Bloody Mary" persona is brutal, sadistic, and hates all men. Aside from highly developed martial arts skills, Walker also possesses telekinetic powers and, more dangerously, pyrokinesis, the ability to set people or objects in her immediate vicinity aflame.

A favorite pawn of the Kingpin, Typhoid did frequent battle (and had a love-hate relationship) with Daredevil before disappearing. Through hypnosis, her abnormal and psychotic personalities were suppressed and Mary Walker's consciousness gained dominance. She then began to lead a normal life, even becoming a soap opera star.

However, this was not to last. The Kingpin fell from power in a violent coup and was left in a coma near death. When he recovered he started rising back to power, taking out his enemies. To distract Daredevil while he retook his criminal empire, the Kingpin paid a visit to Walker while she was doing her show, and with a brunt slap released the abnormal personalities. After confronting Daredevil in his secret identity (Matt Murdock) and setting him on fire, his bodyguards Luke Cage and Jessica Jones managed to take her down. Mary was imprisoned on the 'Raft', a maximum security prison for superpowered criminals.

Electro later led an attack on the Raft, helping the prisoners break out. While the Avengers came on the scene and managed to stop some of the prisoners, Mary was one of the ones that managed to escape. She also had a brief and disturbing relationship with Deadpool.